The US has accused Russia of resuming the war in Syria

High UN officials have called the brutal attack of the Syrian regime against the besieged districts of the Northern city of Aleppo "barbaric".

After the collapse of the short-lived cease-fire, killing at least 85 people and injured more than 300 others, according to activist groups.

Secretary-General ban Ki-moon said at the meeting of the UN Security Council on Sunday that was "shaken" by the military escalation in the besieged Syrian city, and the use of bombs "praises the violence to new depths of barbarism. "Pan added that the use of air strikes, and incendiary weapons and bombs in densely populated areas may amount to war crimes.

At the same time, U.S. Ambassador Samantha Power said that Russia's support of a deadly attack Assad was "barbarism". "The fact that Russia is sponsoring and doing is not fighting terrorism, it is barbaric," she said in the Security Council.

"Instead of trying to keep the peace Russia and Assad started the war. Instead of helping to save lives and to help civilians, Russia and Assad bombed the convoy, hospital and emergency services who are desperately trying to save the life of the people."

Special envoy for Syria Staffan de Mistura echoed the comments of ban Ki-moon, calling the last days "scary". According to him, "last week was one of the worst in Syria for 6 years in the area of this devastating conflict."

U.S. officials have accused Russia of destruction of a humanitarian convoy, while Moscow denies that the Russian and Syrian warplanes were responsible.